The present invention relates to occupancy sensors.
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An occupancy sensor is an energy conservation device designed to detect the presence of human occupant(s) in a given area. When occupancy is sensed, the various electrically-powered loads in that area controlled by the sensor (for example, lights, ventilation, and the like) are energized. When that same area has been unoccupied for a predetermined period of time, the sensor de-energizes the electrical loads that it controls. Occupancy sensors may therefore conserve a great deal of energy in areas where the occupants do not exercise diligence in de-energizing those electrical loads when they leave the area.
Over the last few decades, several events have led to the growth of a large consumer market for energy saving devices including occupancy sensors. First, there has been an increase in public awareness of energy conservation and its beneficial environmental consequences. In addition, there has been increased realization by both private and government-controlled power generation industries of the economic and environmental advantages of energy conservation as a means of meeting peak load power demands. Finally, there have been legislative mandates at the federal, state and local levels for the use of energy conserving devices, such as occupancy sensors, in government and other public buildings.
Occupancy sensors have been successfully designed and tested using a variety of technologies. A brief description of the most widely used occupancy sensor technologies along with the strengths and weaknesses of those technologies follows:
Active Ultrasonic Acoustic Doppler Occupancy Detection.
This technology allows continuous detection of moving objects that reflect ultrasonic acoustic energy. This method of occupancy detection is highly sensitive since it is based on an active source of ultrasonic acoustic energy. An apparatus and method of this type are disclosed in U.S. patent application Ser. No. 08/384,580, filed Feb. 6, 1995, now U.S. Pat. No. 5,640,14, assigned to the same assignee as the present invention and entitled: OCCUPANCY SENSOR AND METHOD FOR OPERATING SAME, the disclosure of which is incorporated herein by reference.
However, this method of occupancy detection has several limitations: first, it is insensitive to motion that is orthogonal to the direction toward the receiver; second it is insensitive to motion generally not in the line of sight of the receiver; third, it is subject to false tripping due to other sources of ultrasonic energy; fourth, it is subject to false tripping due to heating and air conditioning air flow; and finally, it has no means of range discrimination. Since occupancy sensors based on Doppler techniques have no means of range discrimination, a large-distant target moving at approximately the same speed as a smaller, nearby target might have similar target signatures.
Active Electromagnetic Doppler Occupancy Detection
This technology allows continuous detection of moving objects that reflect electromagnetic energy. This method of occupancy detection is highly sensitive since it is based on an active source of electromagnetic energy. However, this method of motion detection also has several limitations: first, it is insensitive to motion that is orthogonal to the direction toward the receiver; second, it is insensitive to motion generally not in the line of sight of the receiver; third, it is subject to false tripping due to other sources of electromagnetic energy; and finally, it has no means of range discrimination.
Passive Audio Acoustic Occupancy Detection
This technology allows continuous detection of objects that emit audio acoustic energy. This method of occupancy detection is quite sensitive but is subject to false tripping due to non-occupant sources of audio acoustic energy such as facsimile machine, telephone and security system tones, automobile and emergency vehicle horns, etc.
Passive Infrared Occupancy Detection
This technology allows continuous detection of moving objects that emit infrared energy. This method of occupancy detection is also quite sensitive even though it is based on passive sensing of moving sources of infrared energy. This method of occupancy detection also has several limitations: first, it is insensitive to sources generally not in the line of sight of the receiver; second, it is subject to being blinded by intense, stationary sources of infrared energy; third, it is subject to false tripping due to rapid fluctuations in the intensity of stationary infrared sources; and finally, it is subject to a detection coverage tradeoff involving the number of lens facets versus detection range.
Position Sensor Based Occupancy Detection
This technology uses one or more mercury switches to sense changes in the physical position of the sensor. This technology has several limitations: first, it is insensitive to minor motion that may be indicative of occupancy; and second, it is inherently a digital (off/on) device.
Piezoelectric Sensor Based Occupancy Detection
This technology senses the changes in the resistance of a piezoelectric sensor to sense occupancy. This technology is subject to false tripping due to changes in temperature.
Significant innovation in the design of occupancy sensors has occurred over the last few decades. The early occupancy sensors utilized primarily analog signal processing techniques. The large area motion sensor described in U.S. Pat. No. 3,967,283 by Clark et. al., issued Jun. 29, 1976, utilized electromagnetic motion detection and was based on analog signal processing techniques. The occupancy sensor described in U.S. Pat. No. 4,661,720 by Cameron, Jr. et. al., issued Apr. 28, 1987, and the low voltage motion sensor for activating a high voltage load described in U.S. Pat. No. 4,820,938 by Mix et. al., issued Apr. 11, 1989, utilized analog signal processing techniques. The variable gain amplifier used in these sensors required manual adjustment. The room occupancy sensor, lens and method of lens fabrication described in U.S. Pat. No. 5,221,919 by Hermans, issued Jun. 22, 1993, utilized passive infrared detection and was based on analog signal processing techniques. The motion detection sensor with computer interface described in U.S. Pat. No. 5,281,961 by Elwell, issued Jan. 25, 1994, utilized active ultrasonic motion detection and was based primarily on analog signal processing techniques. Although easy to design and relatively cheap to implement, the analog filters in these devices had filter response characteristics that drifted with temperature variations and that varied over the lifetime of the various analog filter components. The overall result of using a sensor based on analog signal processing techniques was an occupancy sensor whose performance was unpredictable.
Additionally, the majority of these early occupancy sensors were based on a single sensing technology. Since each technology has its own inherent limitations, these sensors were subject to false tripping due to a variety of sources. For example, ultrasonic Doppler sensors were subject to false trips due to air conditioning and heating system air flow. In addition, since these sensors had no means of range discrimination, they were subject to false trips due to motion outside the desired range of interest. Similarly, passive infrared (PIR) sensors were subject to being blinded by intense, stationary sources of infrared energy. The automatic lighting device described in U.S. Pat. No. 4,751,399 by Koehring et. al. issued Jun. 14, 1988 utilized only acoustic motion detection. This sensor was subject to false tripping due to non-occupant sources of audio acoustic energy such as facsimile machine, telephone and security system controller tones, emergency vehicle and automobile horns, etc. The selective illumination technique described in U.S. Pat. No. 4,225,808 by Saraceni issued Sep. 30, 1980 allowed the use of pressure, ultrasonic motion, microwave, photoelectric and audible sound sensors but failed to combine these technologies to achieve a more reliable sensor with a reduced probability of false tripping. In order to lessen the probability of false trips, the user was often forced to reduce the sensor's sensitivity. The overall result of using a sensor based on a single technology was an occupancy sensor with reduced sensitivity and reliability.
The next generation of occupancy sensors used two or more sensing technologies. These sensors typically required the user to specify a separate activation threshold for each detector technology in the sensor. The digital detector output of each sensor technology was then combined using classical digital logic to detect occupancy. The preset light controller including infrared sensor operable in multiple modes described in U.S. Pat. No. 5,128,654 by Griffin et. al., issued Jul. 7, 1992, used infrared and visible light sensors. The dual technology motion sensor described in U.S. Pat. No. 5,189,393 by Hu, issued Feb. 23, 1993, combined the outputs of its ultrasonic and infrared sensors using classical Boolean AND and OR hardware logic. In general, these multiple sensing technology sensors had better performance than their predecessors but still exhibited a sensitivity-false alarm tradeoff. For example, if the various detector signals were combined using the logical OR function, the overall sensitivity of the sensor increased at the expense of an increased incidence of false trips. On the other hand, if the various detector signals were combined using the logical AND function, the overall incidence of false trips decreased at the expense of decreased sensor sensitivity. Since each sensing technology has its own separate activation threshold, these sensors were often unable to reliably detect motion in marginal cases where one or more sensing technologies observed signal levels just below the user-defined threshold level. The overall result of using these early multiple sensing technology-based occupancy sensors was an improved performance occupancy sensor that was unable to sense occupancy in the more complex marginal sensor signal level situations.
In general, prior art occupancy sensors heretofore known suffer from a number of disadvantages, including:
1. Lack of a sophisticated multiple sensing technology sensor signal conditioning to more completely exploit the advantages of sensing technologies while minimizing disadvantages. The prior art failed to combine the various occupancy sensor detection technologies in a sophisticated fashion to increase the overall probability of occupancy detection while simultaneously lowering the overall probability of false tripping. PA1 2. Lack of adaptive sensor behavior. The prior art failed to produce an occupancy sensor whose performance adapted over time to optimize the sensor's performance. PA1 3. Lack of digital signal processing techniques. The prior art used analog signal processing techniques. The analog filters used in these sensors required manual tuning that was a costly, time consuming process. In addition, the performance of these analog filters was temperature dependent and drifted with time. PA1 4. Lack of means to simply and efficiently communicate the status of the sensor to installation and maintenance personnel. An occupancy sensor, typically has a number of settings that determine its mode of operation, and that the person who installs or maintains the sensor may wish to review. The sensor is typically installed out of reach on a ceiling or wall such that its adjustment knobs or dials are not readily visible. The prior art does not incorporate a system to make such settings readily available and apparent to a person who wishes to query them. PA1 5. Lack of means to check status of the controlled signal to determine if a load device is connected, or if the controlled output is misconnected or shorted. PA1 6. Lack of permanent storage of sensor variables. The prior art failed to permanently store various sensor settings. In the event of a power failure, these sensors had no means of recovering their previous settings. PA1 7. Lack of no means to recognize an excessively reverberant controlled space with excessive ultrasonic return signal amplitude, and lack of means to compensate by adjusting the ultrasonic transmitter amplitude. PA1 8. Lack of ultrasonic receiver preamplifier and demodulator performance monitoring means. The prior art did not monitor ultrasonic receiver preamplifier and demodulator performance and did not have means for making adjustments to accommodate a poorly executed installation or highly acoustically reflective space. A sophisticated ultrasonic sensor incorporates a high gain receiver preamplifier that may become saturated due to excessive acoustic reflections from room walls and other hard structures within the space. Furthermore, the sensor may be installed incorrectly too close to a fixed acoustic reflector such as a wall, exit sign, or other architectural feature. Saturation of the receiver preamplifier causes the motion signal to be lost, and the sensor to be effectively blinded by the excessive signal level. It is desirable that the sensor may be installed by unskilled personnel, and that the sensor be able to accommodate non-ideal situations created either by improper installation or difficult acoustic environments. The prior art has no means to determine saturation of the receiver preamplifier, nor any means to correct for such saturation. PA1 9. Lack of occupancy cycle detection and utilization. The prior art did not detect the typical daily and weekly occupancy cycle of the sensor's environment and use that information to make occupancy decisions. A workspace is typically occupied according to a cycle that varies predictably throughout the day, and also according to a set pattern through the work week. Heretofore, sensors have not taken into account this pattern, and the prior art has no means to survey and record the typical daily and weekly occupancy patterns, nor to store that information, nor to act on the basis of that information. PA1 10. Lack of adaptive PIR sensitivity adjustment to accommodate different and time-varying levels of ambient PIR noise